In a conventional gear coupling having a pinion with external gear teeth and a sleeve with internal gear teeth, a sleeve having openings at both ends has been used. The opening at one end thereof is closed over with an end cover having a hole through which a rotary shaft passes, and the opening at the other end is closed off with a member. At least either one of the openings is as large as the pinion can be introduced into the sleeve. A lubricant leakage prevention mechanism is provided at the joint portion between the sleeve and the member closing off the opening. (Refer to Japanese Patent Laid-Open No. JP-A-7-286622, for example.)
The pinion is ordinarily fixed to rotary shaft by shrink fit process. Since shrink fit cannot be carried out with the pinion remaining inside the sleeve, the gear coupling is assembled by the following steps: first, the pinion is fixed to the rotary shaft by the shrink fit in a state where the rotary shaft has passed through the rotary shaft space of the end cover; second, the pinion is introduced into the sleeve to be engaged with the internal gear of the sleeve; then, the end cover is attached to the sleeve; and finally, the other end opening of the sleeve is closed off.